Preconditioning and stem cell survival.

The harsh ischemic and cytokine-rich microenvironment in the infarcted myocardium, infiltrated by the inflammatory and immune cells, offers a significant challenge to the transplanted donor stem cells. Massive cell death occurs during transplantation as well as following engraftment which significantly lowers the effectiveness of the heart cell therapy. Various approaches have been adopted to overcome this problem nevertheless with multiple limitations with each of these current approaches. Cellular preconditioning and reprogramming by physical, chemical, genetic, and pharmacological manipulation of the cells has shown promise and "prime" the cells to the "state of readiness" to withstand the rigors of lethal ischemia in vitro as well as posttransplantation. This review summarizes the past and present novel approaches of ischemic preconditioning, pharmacological and genetic manipulation using preconditioning mimetics, recombinant growth factor protein treatment, and reprogramming of stem cells to overexpress survival signaling molecules, microRNAs, and trophic factors for intracrine, autocrine, and paracrine effects on cytoprotection.